1. Field
The present disclosure is generally related to an ink limiting method and algorithm. More specifically, this disclosure describes a method for constraining a look up table (LUT) node set by a smaller gamut.
2. Description of Related Art
In general, digital and offset press ink limiting algorithms have been static in technology for many years. Commonly, many known methods operate purely upon the CMY values destined for printing, which defeats color management when outputting images. Standard algorithms that operate on CMYK values only tend to operate without regard for managing the overall look of the image when printed, i.e., without color managing the results, and are primarily focused on reducing hardware operability issues such as: a) wet paper in offset presses, b) fuser overload in electrophotographic printing, and c) fuser curl in electrophotographic printing. Typically, an algorithm truncates CMY ink at specified maximum, while preserving K.
An example of a traditional approach for converting image data of device independent color space, e.g., CIE L*a*b* or RGB, into dependent color space, e.g., CMYK, is GCR (Gray Component Replacement). A GCR approach can be used to calibrate and/or control the total ink amount for CMYK printers (e.g., define the amount of GCR to be applied for any given color). It can include constraining or replacing an amount of the C, M and Y separations with a relative amount of the K separation, or vice versa.
Traditional approaches can be limited in their use with regards to CMYK data, and may not be able to reduce a total ink amount to lower percentage values. Because many ink limit algorithms are not color managed, when aggressive ink limits are placed to reduce ink amounts to lower percentage values (e.g., lower than 150 percent), they tend to eliminate the color managed nature of the workflow. For example, such approaches tend to limit ink amounts, to different values in different regions (i.e., values for C can be different than values for M), thus, resulting in unbalanced color and lesser image quality. Accordingly, standard ink limit algorithm(s) can result in image and color blocking when applying aggressive ink limits, as shown in FIGS. 1-3 and discussed later.
Further, many other visual print artifacts, like unbalanced image print outcomes where chromatic appearance is relevant, can be provided on the output or printed image, resulting in the printed image looking or appearing to be of lesser quality, leaving customers displeased. Other examples of effects on output images by current ink limiting algorithms include, but are not limited to: a) de-saturated red, green, and blue secondary colors that have been “ink limited” coupled with very saturated separations since the single separations at 100% are not affected by even an aggressive ink limit algorithm; b) blocking in dark, off-neutral colors due to dramatic clipped CMYK reduction by the simple algorithm; c) compromise of compression built into the output Look Up Table designed to deal with mismatched dynamic range between data encoding space (like RGB) and print space (CMYK—less dynamic range); and d) eliminating CMYK (values) without regard for color managed outcomes in digital printing. Workflow choices for ink limit can usually be limited to a selection of a number between 0 and 100% (inclusive) during the construction of profiling, but with no feedback on the impact of the ink limit on specific jobs in the workflow.